Cytolytic CD8 Research Articles

Triple bypass: complicated paths to HIV escape

Human immunodeficiency virus (HIV) type 1 is highly efficient at evading immune responses and persisting, ultimately causing fatal immunodeficiency in some patients. Mutation in the epitopes recognized by cytolytic CD8+ T cells (CTLs) is one such escape process. A new study now shows that one HIV-1 escape mutation may also result in impaired dendritic cell (DC) activity, possibly impairing later T cell responses to the same and other epitopes. The new data complete our understanding of the mechanisms by which the CTL response to an immunodominant gag epitope presented by human histocompatibility leukocyte antigen (HLA)-B27 is evaded. The complexity of the full escape helps to explain why patients with this HLA type progress to AIDS more slowly than average.

Genetic modification of T cell clones to improve the safety and efficacy of adoptive T cell therapy.

Our laboratory has developed methods to isolate human antigen-specific cytolytic CD8+ T cell clones and to expand such clones in vitro to numbers sufficient for T cell therapy of human diseases. Studies in immunocompromised bone marrow transplant patients at high risk for disease associated with cytomegalovirus have demonstrated that administration of more than 10(9) CD8+ T cell clones is safe and can effectively reconstitute a deficient human immune response. Our laboratory is applying this strategy of adoptive therapy to the treatment of human cancer, starting with the subset of patients with Hodgkin's disease who show expression of proteins encoded by the Epstein-Barr virus in their malignant Reed-Sternberg cells. The development of efficient systems such as retroviral vectors for the introduction of genes into primary cells has made it possible to consider overcoming some of the limitations of the effector T cells that normally mediate response to an antigen. Our laboratory is attempting to modify T cell clones by the introduction of genes before transfer as a means to improve the safety and/or efficacy of T cell therapy.

4-1BB Is Superior to CD28 Costimulation for Generating CD8+ Cytotoxic Lymphocytes for Adoptive Immunotherapy

Artificial APCs (aAPCs) genetically modified to express selective costimulatory molecules provide a reproducible, cost-effective, and convenient method for polyclonal and Ag-specific expansion of human T cells for adoptive immunotherapy. Among the variety of aAPCs that have been studied, acellular beads expressing anti-CD3/anti-CD28 efficiently expand CD4+ cells, but not CD8+ T cells. Cell-based aAPCs can effectively expand cytolytic CD8+ cells, but optimal costimulatory signals have not been defined. 4-1BB, a costimulatory molecule expressed by a minority of resting CD8+ T cells, is transiently up-regulated by all CD8+ T cells following activation. We compared expansion of human cytolytic CD8+ T cells using cell-based aAPCs providing costimulation via 4-1BB vs CD28. Whereas anti-CD3/anti-CD28 aAPCs mostly expand naive cells, anti-CD3/4-1BBL aAPCs preferentially expand memory cells, resulting in superior enrichment of Ag-reactive T cells which recognize previously primed Ags and efficient expansion of electronically sorted CD8+ populations reactive toward viral or self-Ags. Using HLA-A2-Fc fusion proteins linked to 4-1BBL aAPCs, 3-log expansion of Ag-specific CD8+ CTL was induced over 14 days, whereas similar Ag-specific CD8+ T cell expansion did not occur using HLA-A2-Fc/anti-CD28 aAPCs. Furthermore, when compared with cytolytic T cells expanded using CD28 costimulation, CTL expanded using 4-1BB costimulation mediate enhanced cytolytic capacity due, in part, to NKG2D up-regulation. These results demonstrate that 4-1BB costimulation is essential for expanding memory CD8+ T cells ex vivo and is superior to CD28 costimulation for generating Ag-specific products for adoptive cell therapy.

Gene-Engineered Varicella-Zoster Virus–Reactive CD4+ Cytotoxic T Cells Exert Tumor-Specific Effector Function

T cells with grafted specificities for surface antigens provide an avenue for rapidly producing immune effector cells with tumor specificity. However, the function of chimeric receptor (chRec) gene-modified T cells is limited by lack of T-cell expansion and persistence. We propose to use varicella zoster virus (VZV)-reactive T cells as host for the chRec because these cells can be expanded both in vitro and in vivo by stimulation of their native receptor during endogenous reexposure to the virus or by administration of VZV vaccine. We obtained human T cells reactive with VZV from the peripheral blood of seropositive donors by stimulation with VZV lysate and evaluated their characteristics after genetic modification with two tumor-specific model chRecs. Cultures dominated by cytolytic CD4(+) T cells (VZV-CTL) could be expanded and maintained in vitro. Gene-modified VZV-CTL recognized and lysed tumor targets in a MHC-independent manner while maintaining functional, MHC-restricted interaction with VZV antigen through their native receptor. Thus, chRec-transduced VZV-CTL may provide a source of potent tumor-reactive cells for adoptive immunotherapy of cancer. The availability of a safe and effective VZV vaccine provides the option of repeated in vivo stimulation to maintain high T-cell numbers until the tumor is eliminated.

Expansion of natural killer cell receptor (CD94/NKG2A)–expressing cytolytic CD8 T cells and CD4 +CD25 + regulatory T cells from the same cord blood unit

Cord blood contains a significant number of precursor cells that differentiate to cytotoxic effector cells and immunoregulatory cells. We tried to expand inhibitory natural killer cell receptor CD94-expressing CD8 T cells with cytolytic activity and CD4(+)CD25(+) regulatory T cells from the same cord cell unit. Cytotoxic CD94-expressing CD8 T cells were expanded from CD4-depleted cord blood using an immobilized anti-CD3 monoclonal antibody and a cytokine and also CD4(+)CD25(+) regulatory T cells were expanded from a CD4-enriched fraction derived from the same cord blood unit using anti-CD3/CD28 monoclonal antibody-coated Dynabeads and cytokines. We were able to obtain a more than 1000-fold expansion of CD94-expressing CD8 T cells and a more than 50-fold expansion of CD4(+)CD25(+) cells from the same cord blood unit. These expanded CD4(+)CD25(+) cells expressed FoxP3 mRNA at a level about 100-fold higher than that in isolated CD25(-) cells and could suppress allogeneic mixed lymphocyte culture by >80% (effector cells: CD4(+)CD25(+) cells = 2:1). Cytolytic activities of purified CD94-expressing cells detected by a 4-hour (51)Cr release assay against K562 were >60%. Coculture of CD94-expressing cells with expanded CD4(+)CD25(+) cells did not have any effect on cytolytic activities of purified CD94-expressing cells against K562 cells. These expanded cytolytic CD94-expressing CD8 cells might be able to induce a graft-vs-leukemia effect without enhancing graft-vs-host disease, and CD4(+)CD25(+) cells might be able to suppress allogeneic responses, including graft-vs-host disease and graft rejection after cord blood transplantation.

Potent CTL Induction by a Whole Cell Pertussis Vaccine in Anti‐Tumor Peptide Immunotherapy

Promising yet limited clinical responses have been reported for peptide based immunotherapy against tumors. In order to induce more potent cytolytic CD8 T cell responses, we investigated the use of Bordetella pertussis vaccine as an adjuvant for peptide immunization. A whole cell (Wc) vaccine has been known to induce a Th1 biased immune response while an acellular (Ac) vaccine tends to induce that of the Th2 type. Natural infection by B. pertussis helps to maintain a robust Th1 memory in the host population. To examine the adjuvant activity of the pertussis vaccine, we immunized mice with an ovalbumin peptide as a model tumor antigen, and monitored the development of anti-tumor activities. The addition of either the Ac or the Wc vaccine helped expand the specific CD8 T cells. However, there was a marked difference in the induced cytolytic activity where the Wc vaccine was superior to the Ac. The Wc vaccine was also more effective in inducing in vivo tumor rejection. The adjuvant activity was not only effective against ovalbumin, but was also evident when an endogenous tumor antigen, Wilms' tumor 1 gene product, was targeted. These results indicate that, although the Wc vaccine does not share the same antigen specificity with tumor cells, it can aid in the development of highly cytolytic CD8 T cells as an adjuvant at the site of peptide immunization.

Immunogenicity of the carcinoembryonic antigen derived peptide 694 in HLA-A2 healthy donors and colorectal carcinoma patients

Carcinoembryonic antigen (CEACAM5) is commonly overexpressed in human colon cancer. Several antigenic peptides recognized by cytolytic CD8+ T-cells have been identified and used in colon cancer phase-I vaccination clinical trials. The HLA-A*0201-binding CEA(694-702) peptide was recently isolated from acid eluted MHC-I associated peptides from a human colon tumor cell line. However, the immunogenicity of this peptide in humans remains unknown. We found that the peptide CEA(694-702) binds weakly to HLA-A*0201 molecules and is ineffective at inducing specific CD8+ T-cell responses in healthy donors. Immunogenic-altered peptide ligands with increased affinity for HLA-A*0201 were identified. Importantly, the elicited cytolytic T lymphocyte (CTL) lines and clones cross-reacted with the wild-type CEA(694-702) peptide. Tumor cells expressing CEA were recognized in a peptide and HLA-A*0201 restricted fashion, but high-CEA expression levels appear to be required for CTL recognition. Finally, CEA-specific T-cell precursors could be readily expanded by in vitro stimulation of peripheral blood mononuclear cell (PBMC) from colon cancer patients with altered CEA peptide. However, the CEA-specific CD8+ T-cell clones derived from cancer patients revealed low-functional avidity and impaired tumor-cell recognition. Together, using T-cells to demonstrate the processing and presentation of the peptide CEA694-702, we were able to corroborate its presentation by tumor cells. However, the low avidity of the specific CTLs generated from cancer patients as well as the high-antigen expression levels required for CTL recognition pose serious concerns for the use of CEA694-702 in cancer immunotherapy.

4-1BB is Superior to CD28 Costimulation for Generating Effector CD8+ T Cells for Adoptive Immunotherapy (48.12)

Abstract Artificial APCs (aAPCs) provide a new approach to expand cells for adoptive cell therapy, but optimal requirements for CD8+ expansion have not been defined. Beads expressing αCD3/αCD28 efficiently expand CD4+ cells, but not cytolytic CD8+ T cells. 4-1BB, a costimulatory molecule expressed by a minority of resting CD8+ T cells, is transiently upregulated by all CD8+ T cells following activation. We compared the capacity for aAPCs providing costimulation via 4-1BB vs. CD28 to expand cytolytic CD8+ T cell populations. Whereas αCD3/αCD28 aAPCs preferentially expand naive cells, αCD3/4-1BBL aAPCs preferentially expand memory cells, resulting in cultures with enhanced reactivity to previously primed viral antigens and leading to efficient expansion of electronically sorted CD8+ populations reactive toward viral or tumor-associated antigens. Moreover, using HLA-A2-Fc fusion proteins, 4-1BBL aAPCs selectively induced a 3 log expansion of antigen-specific CTL from polyclonal CD8+ PBL over 14 days; similar expansions were not induced using HLA-A2-Fc/αCD28 aAPCs. Compared to αCD3/αCD28 expanded CD8+ CTL, αCD3/4-1BBL expanded CD8+ T cells also mediate enhanced cytolytic capacity as a result of 4-1BB signaling itself and NKG2D upregulation. These results demonstrate that 4-1BB costimulation is superior to CD28 costimulation for expanding antigen specific CD8+ CTL for use in adoptive immunotherapy.

Biomarkers of CD4+ CTL cell mediated immunity to tuberculosis (43.51)

Abstract The immune responses mediated by interactions between T-lymphocyte subsets and mycobacteria-infected macrophages are critical for control of tuberculosis . In these studies, the bovine model was used to characterize the cytolytic and mycobactericidal CD4+ T cell response induced by BCG vaccination. Antigenic stimulation of CD4+ T-cells from BCG vaccinated cattle induced expression of perforin and IFNgamma in cells expressing a CD45RA−, CD45RO+, and CD62L+ cell surface phenotype. Antigen specific enhancement of granulysin, IFNgamma, perforin, IL-4, IL-13, and IL-21 mRNA expression was detected and not detected for IL-2, IL-6, IL-10, IL-15, TNFα, FasL, and CD40L. Following antigenic stimulation, CD4+ T cells from BCG vaccinated animals contributed to reduction of intracellular BCG in infected macrophages. These results demonstrate that vaccination with BCG induces a subpopulation of mycobacteria-specific CD4+ T cells that are characterized by the expression of a cell-surface memory phenotype, enhanced expression of mycobactericidal molecules, and anti-mycobacterial activity against intracellular M. bovis. This work was supported by the NIAID Fellowship for Training in Emerging and Re-emerging Infectious Disease and the Sealy Center for Vaccine Development, UTMB, the Texas-United Kingdom Collaborative Research Initiative, and the Institute for Animal Health by DEFRA and the BBSRC, UK.

Pediatric CD56+ Anaplastic Large Cell Lymphoma: A Review of the Literature

Anaplastic large cell lymphomas (ALCLs) are a heterogeneous group of CD30+ large cell lymphomas that, according to the World Health Organization classification, are defined as being of T-cell origin, based on immunophenotype, and/or the finding of a T-cell gene rearrangement by molecular studies. Most cases express cytotoxic granule-associated proteins. Relatively recent data have suggested that some T-cell ALCLs are derived from cytolytic CD4+ cells, gammadelta T cells, or natural killer-like (CD56+ or CD57+) T cells. We encountered a pediatric case of CD56+, anaplastic lymphoma kinase-positive ALCL of apparent natural killer-like T-cell origin (showing positivity for CD2, cytoplasmic CD3, surface CD3 partial positivity, CD7, CD8, CD56, TIA-1, and granzyme B). The patient had initial lymph node and multiple sites of cutaneous involvement and an aggressive clinical course with multiple recurrences after varying periods of complete remission. To review the current pediatric literature regarding the incidence, differential diagnosis, and clinical course of such cases. Relevant articles indexed in PubMed (National Library of Medicine) between 1975 and 2006. Our review did not confirm a uniformly aggressive clinical course in pediatric cases of CD56+ ALCLs. Such cases suggest the usefulness of the analysis of CD56-positivity in additional cases of ALCL in an attempt to accrue additional information on this condition. Future accrual of such cases may address whether such cases should be treated more aggressively or with possible targeted therapeutic regimens.

Expansion of Inhibitory NK Receptor (CD94/NKG2A)-Expressing Cytolytic CD8 T Cells and CD4+CD25+ Regulatory T Cells from the Same Cord Blood.

It has recently been shown that inhibitory natural killer cell receptors (NKRs) on not only NK cells but also on T cells negatively regulate NK cell and T cell functions through their binding to MHC class I molecules. The C-type lectin superfamily inhibitory NKR CD94/NKG2A heterodimer recognizes an HLA-E that preferably bound to a peptide derived from the signal sequences of most HLA class I. Therefore, CD94-expressing cells can monitor the global status of HLA class I on the tumor and leukemic cells and induce cytolytic attack without inhibitory signal against HLA class I decreased target cells resulting induction of graft-versus-leukemia (GVL) effect but does not attack normal cells with HLA class I expression resulting no enhancement of graft-versus-host disease (GVHD). On the other hand, CD4+ CD25+ regulatory T cells (Treg) contribute to suppress allogeneic immune responses and prevent transplant rejection and GVHD. In this study, we tried to expand CD94-expressing T cells and Treg cells from the same cord blood cells and then investigated their cytolytic characteristics and immunoregulatory function in order to develop a potential strategy of cell therapy for hematological malignancy.After CD4 enrichment by negative selection using magnetic cell sorting (MACS) (Miltenyi Biotec)(CD4-enriched fraction) from cord blood, CD4+ CD25+ cells were isolated by positive selection with anti-CD25 magnetic microbeads. We could get more than 1,000 fold expansion of CD94-expressing CD8 T cells from CD4-depleted fraction after 8 days culture with immobilized anti-CD3 monoclonal antibody (mAb) (1 μg/mL) and IL-15 (5 ng/mL). Isolated CD4+ CD25+ cells were cultured with anti-CD3/CD28 mAb-coated dynabeads and IL-15 (5 ng/mL) and we could get about 50 fold expansion of Treg cells for 8 days. These expanded Treg cells could suppress allogeneic mixed lymphocyte culture more than 80% (effector cells: Treg cells= 2:1) and expressed FoxP3 mRNA about 100 fold compared with isolated CD25-negative cells. Cytolytic activities of purified CD94-expressing cells (CD94 > 90%) detected by 4 hours 51Cr release assay against K562 were 68.8 ± 16.8 % (n=5). Coculture of CD94-expressing cells with expanded Treg cells (CD94-expressing cell: Treg cells= 1:1, preincubation 4 hours) did not have any effect on cytolytic activities of purified CD94-expressing cells against K562 cells (66.1 ± 19.8 %, n=5). CD94-expressing CD8 T cells with cytolytic activity could be expanded from CD4-deplted fractions and Treg cells with immunosuppressive activity and increased expression level of FoxP3 mRNA could be expanded from CD4-enriched fractions of the same cord blood. Expanded these cytolytic CD94-expressing CD8 cells might be able to induce GVL effect without enhancing GVHD and Treg cells might be able to suppress allogeneic response including GVHD and graft rejection. Therefore, this strategy may be useful to differentiate lymphocytes in cord blood to two different kinds of effector cells exhibiting cytolytic or immunoreguratoly characters.

Non-Hodgkin Lymphoma B-Cells Induce Intratumoral CD4+CD25− T Cells To Express Foxp3 and Gain Regulatory Function.

We have previously shown that CD4+CD25+Foxp3+ regulatory T cells from NHL tumors suppress the function of infiltrating CD4+ T cells and cytolytic CD8+ T cells. Expression of Foxp3 has been demonstrated to be crucial to the development and function of CD4+CD25+ regulatory T cells. However, the mechanistic details that drive development of Foxp3 expression in T cells, in both the normal and malignant scenario, remains to be fully elucidated. Previous studies suggest that Foxp3 expression in CD4+CD25− T cells can be upregulated by tolerizing stimuli such as activation through TCR, corticosteroids, estrogen, and TGF-beta. Because lymphoma B cells have been shown to induce T-cell tolerance, we postulated that lymphoma B cells may play a role in the generation of regulatory T cells by inducing Foxp3 expression in CD4+CD25− T cells.FoxP3 expression was initially thought to be restricted to CD4+CD25+ regulatory T cell population. However, recent literature suggests that Foxp3 may also be expressed in CD4+CD25− T cells. Using biopsy specimens from patients with B-cell NHL, we found that a subset, 15%, of infiltrating CD4+CD25− T cells express Foxp3 and are capable of suppressing the proliferation and granule production of infiltrating cytotoxic CD8+ T cells. These initial studies suggest that CD4+CD25−Foxp3+ T cells have regulatory function. To explore the underlying mechanism by which Foxp3 expression is regulated, we determined the effect of costimulatory signals on Foxp3 expression in CD4+CD25−Foxp3− T cells. Activation with OKT3/anti-CD28 Ab as well as DC-mediated activation induced Foxp3 expression in a subset of CD4+CD25− T cells. We also found that the presence of lymphoma B cells during activation augmented the induction of Foxp3 expression in CD4+CD25− T cells and that NHL B cell-mediated Foxp3 expression was cell contact-dependent. To better understand the contribution of NHL B cells in Foxp3 expression, we explored the possibility that CD27-CD70 interaction may be involved in Foxp3 expression. Lymphoma B cells express CD70, but not B7-1 and B7-2, which have been shown to be important in protecting tumor cells from lysis and contributing to cancer pathogenesis. Ligation of CD27 by receptor cross-linking enhanced Foxp3 expression in infiltrating CD4+CD25− T cells in B-cell NHL.Taken together these studies reveal a novel role for NHL B cells in development of regulatory T cells. Our data show that lymphoma B cells induce expression of Foxp3 in infiltrating CD4+CD25− T cells and may result in development of T cells with regulatory function within the tumor microenvironment. Our results also suggest a potential role for CD27-CD70 interactions in this process. The ability of malignant B cells to drive development of regulatory T cells may be one mechanism by which lymphoma B cells protect themselves from anti-tumor immunity. (Supported in part by the Iowa/Mayo Lymphoma SPORE CA97274).

Presentation of Epstein Barr Virus (EBV) Epitopes by Activated Human γδ T Cells Induces Peptide-Specific Cytolytic CD8+ T Cell Expansion.

Efficient antigen presentation is an important prerequisite for the induction of T cell mediated immunity against viral and tumor antigens. The functional heterogeneity, limited availability and poor expansion of dendritic cells (DC) has motivated a search for alternative sources of antigen-presenting cells (APC). Bisphosphonate-activated human γδ T cells were shown to function as APC by inducing primary T cell responses to allogeneic and microbial antigens. Here, we extended these observations by investigating the capacity of activated γδ T cells to present Epstein Barr virus lytic cycle and latency antigens in a peptide-specific manner and induce expansion of fully functional, virus-specific cytotoxic αβ T cells. Peripheral blood-derived γδ T cells were expanded from three individual healthy donors by stimulation with the aminobisphosphonate zoledronic acid (1 μg/ml) in the presence of rhIL-2 (100 U/ml) and rhIL-15 (10 ng/ml). Under these conditions, γδ T cells (Vγ9+Vδ2+) acquired a phenotype characteristic for APC, including upregulation of HLA-DR as well as the costimulatory ligands CD80, CD83, CD86, CD40, and 4-1BBL (CDw137L). Whereas expression of most markers decreased after peak levels were reached on day 5, CD86 and HLA-DR remained upregulated on >80% of the cells for prolonged culture periods of >14 days. We next assessed the APC function of activated γδ T cells by testing their ability to stimulate expansion of antigen-specific cytotoxic T cells in vitro. Autologous peripheral blood lymphocytes (PBMC) were incubated with activated γδ T cells pulsed with the HLA-B8-restricted epitope of the EBV lytic cycle antigen BZLF1 (RAKFKQLL). We demonstrated selective expansion of RAK-pentamer-specific CD3+ CD8+ T cells to a mean of 15% (range 6–24%) on day 10. BZLF-1 represents a highly immunogenic virus antigen, whereas the EBV latency-associated antigen LMP-2a is less T cell-stimulatory and, due to its expression on Hodgkin′s lymphoma cells, is an important target for tumor-specific immune therapy. Stimulation of PBMC with γδ T cells pulsed with the HLA-A2-restricted LMP2a epitope FLYALALLL also resulted in a substantial increase of pentamer-reactive T cells to a mean of 3.5% (1.4–5.5%), which was comparable to the increase obtained when peptide-loaded autologous DC were used (mean of 3.5%; range 1.2–5.7%). γδ T cell stimulation in the absence of peptide failed to induce specific T cell expansion (mean of 0.1%; 0.03–0.15%). CD8+ T cells expanded against EBV-peptide-pulsed activated γδ T cells functionally interacted with peptide-loaded autologous DC or lymphoblastoid cell lines (LCL), as demonstrated by efficient and specific MHC class I-restricted cytolysis of 41–65% at an effector-target ratio of 40:1. Peptide-specific cytotoxic T cell functionality was comparable to that obtained with T cells expanded in the presence of pulsed autologous DC from the same donors. In summary, bisphosphonate-activated γδ T cells are potent antigen-presenting cells for reproducible expansion of disease antigen-specific CTL. Thus, they represent a novel source of highly efficient professional APC for antigen-specific immunotherapy of viral or malignant disease.

Kinetics of CD8+ effector T cell responses and induced CD4+ regulatory T cell responses during Friend retrovirus infection

Cytolytic CD8+ T cells are critical for the control of acute Friend virus (FV) infection yet they fail to completely eliminate the virus during chronic infection because they are functionally impaired by regulatory T cells (Treg). We performed a kinetic analysis of T cell responses during FV infection to determine when dysfunction of CD8+ T cells and suppressive activity of CD4+ regulatory T cells develops. At 1 week post infection, virus-specific CD8+ T cells with effector phenotype and cytolytic potential expanded. Peak expansion was found at 12 days post infection, correlating with peak viral loads. After 2 weeks when viral loads dropped, numbers of activated CD8+ T cells started to decline. However, a population of virus-specific CD8+ T cells with effector phenotype was still detectable subsequently, but these cells had lost their ability to produce granzymes and to degranulate cytotoxic molecules. Contemporaneous with the development of CD8+ T cell dysfunction, different CD4+ T cell populations expressing cell surface markers for Treg and the Treg-associated transcription factor Foxp3 expanded. Transfer as well as depletion experiments indicated that regulatory CD4+ cells developed during the second week of FV infection and subsequently suppressed CD8+ T cell functions, which was associated with impaired virus clearance.

Organ- and Disease-Stage-Specific Regulation ofToxoplasma gondii-Specific CD8-T-Cell Responses by CD4 T Cells

Toxoplasma gondii induces a persistent central nervous system infection, which may be lethally reactivated in AIDS patients with low CD4 T-cell numbers. To analyze the role of CD4 T cells for the regulation of parasite-specific CD8 T cells, mice were infected with transgenic T. gondii expressing the CD8 T-cell antigen beta-galactosidase (beta-Gal). Depletion of CD4 T cells prior to infection did not affect frequencies of beta-Gal(876-884)-specific (consisting of residues 876 to 884 of beta-Gal) CD8 T cells but resulted in a pronounced reduction of intracerebral beta-Gal-specific gamma interferon (IFN-gamma)-producing and cytolytic CD8 T cells. After cessation of anti-CD4 treatment a normal T. gondii-specific CD4 T-cell response developed, but IFN-gamma production of intracerebral beta-Gal-specific CD8 T cells remained impaired. The important supportive role of CD4 T cells for the optimal functional activity of intracerebral CD8 T cells was also observed in mice that had been depleted of CD4 T cells during chronic toxoplasmosis. Reinfection of chronically infected mice that had been depleted of CD4 T cells during either the acute or chronic stage of infection resulted in an enhanced proliferation of beta-Gal-specific IFN-gamma-producing splenic CD8 T cells. However, reinfection of chronically infected mice that had been depleted of CD4 T cells in the acute stage of infection did not reverse the impaired IFN-gamma production of intracerebral CD8 T cells. Collectively, these findings illustrate that CD4 T cells are not required for the induction and maintenance of parasite-specific CD8 T cells but, depending on the stage of infection, the infected organ and parasite challenge infection regulate the functional activity of intracerebral CD8 T cells.

P‐8 THE LOCAL IMMUNE RESPONSE TO LOW‐GRADE CIN – ALTERATIONS IN T‐CELL AND MACROPHAGE SUBSETS

Introduction: Despite the cervix having the largest concentration of lymphocytes and macrophages in the lower genital tract, there is limited knowledge of these cell types in CIN. This study was undertaken to compare T‐cell and macrophage populations in women with and without low‐grade CIN.Methods: Control group: 10 women with a normal recent cervical smear result, mean age 30 years. Study group: 10 women with low‐grade CIN, mean age 33.2 years. Colposcopically directed cervical biopsies were taken from control women and from areas of CIN in the study group, and studied using immunoperoxidase and immunofluorescence staining.Results: T‐cell numbers remained constant. In CIN, there were increased proportions of recruited (CD8+CD5+), activated (CD8+HLA‐DR+) and cytolytic (CD8+TIA‐1+) CD8 T‐cells. There were more activated CD4+HLA‐DR+ T‐cells in CIN. Memory T‐cell (CD8+CD45RO+ and CD4+CD45RO+) proportions were reduced. Total macrophage numbers (CD68+) remained constant, but activated macrophages (CD68+HLA‐DR+) rose. Phagocytic (RFD7+) macrophage proportions decreased with a concomitant increase in suppresser macrophages (RFD1+RFD7+).Discussion: Despite cellular numbers remaining unchanged, there were significant changes in T‐cell and macrophage populations in women with low‐grade CIN. There is recruitment of activated and cytolytic CD8 T‐cells. The swing to a predominantly suppressive macrophage phenotype may predispose to CIN. Carcinoma of the cervix occurs more frequently in women who are immunosuppressed. Our data suggests that local and systemic immune mechanisms may be relevant in the response to HPV‐induced neoplasia.

Mirasol PRT treatment of donor white blood cells prevents the development of xenogeneic graft‐versus‐host disease in Rag2–/–γc–/– double knockout mice

Mirasol PRT (Navigant Biotechnologies) treatment utilizes exposure to light in the presence of riboflavin to introduce irreparable lesions to nucleic acids thereby inhibiting pathogen and WBC replication. The ability of Mirasol PRT-treated mononuclear cells (MNCs) to generate xenogeneic graft-versus-host disease (GVHD) responses was used to model transfusion-associated GVHD (TAGVHD). Pairs of human MNCs from five different individual donors that had or had not received Mirasol PRT treatment and contained 30 x 10(6) CD3+ cells were injected intraperitoneally into sublethally irradiated (350 cGy) Rag2(-/-)gamma c(-/-) double-knockout mice. Recipient mice were weighed and observed regularly and euthanized when they exhibited symptoms of GVHD or at termination of the experiment. Recipient lymphoid compartments were collected and phenotyped for the presence of human lymphoid cells. The presence of human cytokines and/or immunoglobulins in the recipient plasma was also used to detect the presence of human cells. Twelve of 14 mice injected with untreated cells developed xenogeneic GVHD, whereas 0 of 14 mice injected with Mirasol PRT-treated cells developed xenogeneic GVHD. End-stage xenogeneic GVHD in the recipients of untreated cells was characterized by the presence of splenic human cytolytic CD4+ and CD8+ cells, with high levels of interferon-gamma, interleukin-10, and xenoreactive antibodies in the plasma. Mirasol PRT treatment of the donor MNCs abolished xenogeneic GVHD responses, indicating that the use of Mirasol PRT treatment of blood products should prevent the development of TAGVHD.

IL-6 drives T cell proliferation

Hyperresponsiveness to the IL-6 family of cytokines triggers a spontaneous rheumatoid arthritis (RA)-like disease in mice. On page 1459, Sawa and colleagues show that excessive IL-6 signaling drives hyperproliferation of CD4+ T cells, which then attack the joints. IL-6 has been implicated in RA and other T cell–driven autoimmune diseases. Indeed, a previous study by this group showed that an activating mutation in the gp130 subunit of the IL-6 receptor caused a lymphocyte-driven arthritis in mice. But the mechanism was unclear. The authors now show that disease development in these mice depends on CD4+ T cells, but not on cytolytic CD8+ T cells or antibody-producing B cells. The CD4+ cells did not appear to cause disease because of an affinity for joint-specific antigens. Rather, the cells simply proliferated excessively in the mutant mice. This hyperproliferation was not the fault of the T cell, as wild-type CD4+ T cells also multiplied excessively and caused disease when transferred into irradiated mutant mice. Rather, the gp130 mutation caused nonhematopoietic cells to produce excess IL-7—a growth factor that triggers T cell proliferation. This is the first evidence that IL-6 family cytokines can trigger IL-7 production. These data suggest that IL-6, which is elevated in the serum and joints of patients with RA, might exacerbate disease by inducing IL-7 and thus driving T cell activation. What causes the overstimulated T cells to attack the joints in the first place remains a mystery.

Virus-specific CD4+ T cells: ready for direct attack

CD4+ T cells are classically thought to orchestrate adaptive immune responses. But recent studies demonstrate that they can also kill infected cells directly. A new paper shows that highly efficient processing of Epstein Barr virus (EBV) glycoproteins for presentation on MHC class II makes virus-transformed B cells susceptible to lysis by CD4+ T cells. Thus, antiviral vaccines should aim to stimulate both helper and cytolytic CD4+ T cells.

Inhibition of Interferon-γ Signaling in Oligodendroglia Delays Coronavirus Clearance without Altering Demyelination

Infection of the central nervous system (CNS) by the neurotropic JHM strain of mouse hepatitis virus (JHMV) induces an acute encephalomyelitis associated with demyelination. To examine the anti-viral and/or regulatory role of interferon-γ (IFN-γ) signaling in the cell that synthesizes and maintains the myelin sheath, we analyzed JHMV pathogenesis in transgenic mice expressing a dominant-negative IFN-γ receptor on oligodendroglia. Defective IFN-γ signaling was associated with enhanced oligodendroglial tropism and delayed virus clearance. However, the CNS inflammatory cell composition and CD8+ T-cell effector functions were similar between transgenic and wild-type mice, supporting unimpaired peripheral and CNS immune responses in transgenic mice. Surprisingly, increased viral load in oligodendroglia did not affect the extent of myelin loss, the frequency of oligodendroglial apoptosis, or CNS recruitment of macrophages. These data demonstrate that IFN-γ receptor signaling is critical for the control of JHMV replication in oligodendroglia. In addition, the absence of a correlation between increased oligodendroglial infection and the extent of demyelination suggests a complex pathobiology of myelin loss in which infection of oligodendroglia is required but not sufficient.